Devices with microelectrode arrays for bio-sensing purposes have an important role in the areas of diagnostic such brain monitoring or in vitro cell monitoring. Conventional microelectrode sensing arrays may include, for example, neural probes, which are used to measure neural activity at one or more sites of the brain.
Conventional neural probes comprise a probe base and a shank, the shank extending from the base for insertion into a portion of the brain. In some cases, electrodes are disposed along the length of the shank, each electrode being adapted to measure a voltage, corresponding to neural activity, in the immediate vicinity of the electrode. In use, the probe base may be positioned on the outside of the brain and comprises base circuitry suitable for recording voltages present at the electrodes of the shank. The base circuitry may further comprise further processing circuitry, for example, a filter or digitization circuitry.
A neural probe will usually comprise shank wires positioned in the shank and connecting an electrode to the base circuitry. As the width of the shank is generally extremely narrow, to reduce potential damage to the brain, there is a maximum limit on the number of shank wires that may be in a shank. This is due to the physical limitations in positioning shank wires, the difficulty in fabricating sufficiently small shank wires and possible complications due to capacitive coupling between closely spaced shank wires.
It is clear that a limitation on shank wires induces a proportional limit on the allowable number of electrodes that may be permitted on the available area for the electrodes. However, it is desirable to allow the electrode area to have an increased number of electrodes in order to acquire more information from regions near to that electrode area. A similar problem arises when implementing a very high density two-dimensional microelectrode arrays which can be conceived as rows of one-dimensional shank. A microelectrode array of this kind, with very limited space between the rows, will also have limited number of wires to carry the signal to a base area placed outside the array.